Telephone calls (so-called nuisance calls) have been increasing rapidly to an indefinite number of telephones for the purposes of sales or solicitation of goods, and therefore effective countermeasures are desired.
As one known technique regarding nuisance call countermeasures, a database (blacklist) of telephone numbers used for nuisance calls has been made, and an incoming call from the telephone number is rejected (for example, refer to Document 1). In reality, when incoming nuisance calls are rejected using the database, calls from telephone numbers that are not registered in the database are received. Therefore, a technique has been proposed recently in which phone call speech is analyzed and nuisance calls are determined early.
As a known technique regarding the above nuisance call countermeasures, when voice recognition is performed during a telephone call and a particular keyword is detected, it is reported that the nuisance call is received using electronic mail etc. to an address that has been previously specified (for example, refer to Document 2).
Further, as another known technique regarding nuisance call countermeasures, an evaluation value representing a degree of stress etc. of a speaker is calculated based on a statistical amount of pitch and power of call speech and an abnormal state of the speaker is detected based on the evaluation value (for example, refer to Document 3).
Document 1: Japanese Laid-open Patent Publication No. 2013-214963
Document 2: Japanese Laid-open Patent Publication No. 2012-70218
Document 3: Japanese Laid-open Patent Publication No. 2013-11830